Thermodynamic control of halogen-terminated silicon nanoparticle morphology

The fabrication of silicon nanoparticles terminated with halogen species provides a convenient route to create readily functionalizable nanostructures; however, the relationship between formation conditions and the thermodynamic ground-state morphology of the nanoparticles thus formed remains poorly understood. In this work, we use density functional theory calculations to compute surface energies of silicon surfaces terminated with fluorine, chlorine, bromine, and iodine as a function of halogen chemical potential and hence we compute, via a nanomorphology model, the thermodynamically optimal morphology of halogen-terminated silicon nanoparticles. We predict a variety of optimal nanoparticle shapes consisting primarily of Si(100), Si(113), and Si(111) facets with varying terminations, and we demonstrate how control over morphology may be attained by controlling the chemical environment. Implications for the fabrication of nanoparticles with facet-selective reactivity are also discussed.